Sessions recused himself Thursday from any investigations pertaining to "any matters related in any way to the campaigns for President of the United States." Top Democrats, including Senate Minority Leader Chuck Schumer and House Minority Leader Nancy Pelosi, have called for Sessions to step down from his post at the Justice Department. Pelosi has charged that Sessions perjured himself in front of Congress.

But experts say that while Sessions' may have misled the Senate Judiciary Committee during his confirmation hearings, his comments likely don't amount to perjury

"Whoever, having taken an oath before a competent tribunal, officer, or person, in any case in which a law of the United States authorizes an oath to be administered, that he will testify, declare, depose, or certify truly, or that any written testimony, declaration, deposition, or certificate by him subscribed, is true, willfully and contrary to such oath states or subscribes any material matter which he does not believe to be true."

In plain English, perjury means willfully lying in a court after taking an oath, which Sessions took at his confirmation hearing.

However, perjury is a "very difficult charge to prove," Laurie L. Levenson, a former federal prosecutor and a professor at Loyola Law School, told Business Insider.

The key question is whether it can be proved Sessions was "willfully untruthful" during the January confirmation hearing, Darryl K. Brown, a law professor at the University of Virginia, told Business Insider.

al franken

(Sen. Al Franken on Capitol Hill.Photo by Drew Angerer/Getty Images)

Take a look at the exchange with Sessions and Sens. Al Franken of Minnesota and Patrick Leahy of Vermont during the hearing:

Franken: "If there was any evidence that anyone affiliated with the Trump campaign communicated with the Russian government in the course of this [2016] campaign, what would you do?"

Sessions: "I'm not aware of any of those activities. I have been called a surrogate at a time or two in that campaign and I did not have communications with the Russians."

Leahy: "Several of the President-elect's nominees or senior advisers have Russian ties. Have you been in contact with anyone connected to any part of the Russian government about the 2016 election, either before or after Election Day?"

Sessions: "No."

While Franken contended Thursday that Sessions' comments were "extremely misleading," he stopped short of invoking "perjury." It's much more difficult to prove that Sessions, a trained attorney, actually lied with intent.

In order to obtain a perjury conviction, the prosecution must make explicitly clear what each specific term in Franken's question means, including what was meant by "affiliated," Stan Brand, senior counsel at Akin Gump and an expert on congressional investigations, told Business Insider.

"The government would have to prove that he [Sessions] understood what the questioner meant by that term, and any ambiguity will be resolved in favor of the witness," Brand added. "As a result I think the viability of a perjury charge is dubious at best."

Sergey Kislyak

(Sergey Kislyak, Russian Ambassador to the United States looks on during a press conference on nuclear non-proliferation at United Nations headquarters October 24, 2008 in New York City.Getty Mario Tama)

Brand added that "inartful or imprecise questions," susceptible to multiple meanings, "cannot sustain a conviction." In other words, Franken's question at the hearing was open to enough interpretation that it would be exceedingly difficult to prove that Sessions perjured himself.

"He might claim he forgot about those meetings," said Brown, the UVA professor. "More likely, he might claim he did not convey information between the ambassador and the Trump campaign during those meetings."

"That is the question that Sen. Franken asked me at the hearing, and that's what got my attention. As he noted, it was first just breaking news and it got my attention, and that is the question I responded to," he said. "I did not respond to the two meetings, one very brief as a speech ... where no such things were discussed. My reply to the question of Sen. Franken was honest and correct as I understood it at the time."

There are grounds for perjury only if it can be proven that Sessions made a false statement, said Levenson, the former federal prosecutor and Loyola Law School professor.

And "almost no one is prosecuted for lying to Congress," P.J. Meitl, the author of a 2007 Quinnipiac Law Review study on perjury charges related to Congress, told Reuters.

The study found that only six people have been convicted of perjury for lying to Congress since the 1940s.

"If he was technically telling the truth, or he can argue that he thought he was answering a different question, then it is unlikely you would see a perjury charge," Levenson added.